The present invention relates generally to the field of magnetic data storage and retrieval systems. In particular, the present invention relates to a thin film transducing head having its studs and electrical bond pads formed of a material selected to reduce thermal deformation.
In a magnetic data storage and retrieval system, a thin film transducing head typically includes a transducer and a substrate upon which the transducer is built. The transducer, which typically includes a writer portion for storing magnetically-encoded information on a magnetic media and a reader portion for retrieving that magnetically-encoded information from the magnetic media, is formed of multiple layers successively stacked upon the substrate. The volume of the transducer is typically much smaller than the volume of the substrate.
The layers of the transducer, which include both metallic and insulating layers, all have differing mechanical and chemical properties than the substrate. These differences in properties affect several aspects of the transducer. First, the layers of the transducing head will be lapped at different rates. Thus, when an air bearing surface (ABS) of the transducing head is lapped during its fabrication, differing amounts of the layers will be removedxe2x80x94resulting in the transducing head having a uneven ABS. Commonly, a greater amount of the metallic layers of the transducer will be removed during the lapping process than will be removed from the substrate. Thus, this lapping process results in a Pole Tip Recession (PTR) of the metallic layers of the transducer with respect to the substrate. The PTR of a particular layer is defined as the distance between the air bearing surface of the substrate and the air bearing surface of that layer.
The differing mechanical and chemical properties of the substrate and transducer layers further affect the air bearing surface during operation of the transducing head. As the magnetic data storage and retrieval system is operated, the transducing head is subjected to increasing temperatures within the magnetic data storage and retrieval system. In addition, a temperature of the transducing head itself, or a part thereof, may be significantly higher than the temperature within the magnetic data storage and retrieval system due to heat dissipation caused by electrical currents in the transducer.
The coefficient of thermal expansion (CTE) of materials used in forming the substrate is typically much smaller than the CTE of materials used in forming the metallic layers of the transducer. Due to the larger CTE of the transducer""s metallic layers, those layers will tend to expand a greater amount than will the substrate. Thus, when the transducing head is subjected to higher operating temperatures, the metallic layers tend to protrude closer to the magnetic disc than the substrate; thereby affecting the PTR of the transducer. This thermal protrusion of the metallic layers, or change in PTR caused by temperature, is referred to as Thermal PTR (T-PTR).
During operation of the magnetic data storage and retrieval system, the transducing head is positioned in close proximity to the magnetic media. A distance between the transducer and the media is preferably small enough to allow for writing to and reading from a magnetic medium having a large a real density, and great enough to prevent contact between the magnetic media and the transducer. Performance of the transducer depends primarily on this distance.
Although T-PTR is largely driven by the large CTE of the metallic layers of the transducer, other large metallic components of the transducing head have a significant impact on T-PTR. Such large metallic components include a plurality of electrical bond pads that function to provide current to the transducer and a plurality of studs that function to provide electrical connection between the individual layers of the transducer and the electrical bond pads. Traditionally, the electrical bond pads are formed of either gold or a bilayer of gold and permalloy. Gold is commonly used for the bond pads because it ensures good electrical contact with external current sources. The studs are conventionally formed of copper for its ease of fabrication. Gold, copper, and permalloy each have a CTE substantially greater than the CTE of materials typically used to form the substrate. Thus, at higher operating temperatures, the bond pads and studs tend to expand more than the substrate. And, as transducing heads have become smaller, the studs and bond pads have been moved closer to the transducer, and have begun having a more pronounced effect on T-PTR.
A transducing head formed upon a slider has a transducer, an electrical contact layer, a stud electrically connected to the contact layer, and a bond pad electrically connected to the stud. The electrical contact layer is electrically connected to the transducer. The stud is formed of a material having a coefficient of thermal expansion less than about 1.3 times a coefficient of thermal expansion of a slider material forming the slider. The bond pad has a metallic underlayer and a top layer. The metallic underlayer is formed of a material having a coefficient of thermal expansion less than about 1.1 times the coefficient of thermal expansion of the slider material.